Finishing of workpieces



Jan. 5; 1954 Filed June 1, 1950 P. K. A. CUPPERS FINISHING OF WORKPIECES2 Sheets-Sheet 1 I77 we 7? 2 0 P502 KIA. Cup vars Jam 1954 P. K. A.CUPPERS 2,564,676

FINISHING OF WORKFIECES Filed June 1, 1950 2 Sheets-Sheet 2lfilmlllllllllll/ I 7 8s 84 Iwveflfm- PduZ KACu o are Patented Jan. 5,1954 FINISHING OF WORKPIECES Paul K. A. Ciippers, Geislingen (Steige),Germany, assignor to Wurttembergische Metallwarenfabrik, Geislingen(Steige), Germany Application June 1, 1950, Serial No. 165,423

15 Claims. (01. 51-7) This invention relates to improved means and amethod for finishing the surface of workpieces as by grinding, polishingor the like, with the aid of tool means which are relatively moved pastthe surfaces of the workpieces which are to be treated.

It is an object of the invention to provide means which permit suchfinishing treatment in a very economical manner.

A special object of the invention is to provide means for finishing thesurface of workpieces extending in different planes or having intricateshapes, ornaments or the like. By Way of example, such a workpiece maybe in the form of a spoon or other piece of cutlery, which is to befinished primarily in order to obtain a neatly ground and polishedsurface, but it is also contemplated to finish in accordance with theinvention workpieces requiring accurate grinding, such as in case ofround journals or the like.

The working and finishing of the surfaces of such workpieces, moreparticularly of an intricate shape, by means of rigid or resilientgrinding discs is elaborate, time-wasting and expensive, since theworkman has to press the workpieces onto the grinding disc by hand,possibly adding a grinding agent, such as, sand, emery, pumice powder,corundum or the like, moving them to and fro in accordance with thevarying contours of the surface. This method is of poor efliciency, yetit requires very much physical force and skill and is very unwholesome.The working of such workpiece surfaces in rotary drums or by means ofsand blast is too course and, therefore, unsuitable for the productionof ground surfaces and smooth, bright surfaces.

It is an important object of the present invention to provide means andmethods for removing the drawbacks of the conventional finishingmethods.

With this and further objects in view, according to the presentinvention the working tool serving for the finishing of workpiecesurfaces is formed by a loose mass of a grinding, polishing or otherworking agent, preferably in a powderous, granular or pasty state, whichmass isconfined in a vessel orpan at least partly surrounding it(hereinafter referred to as the tool vessel or tool pan), and kept underpressure during its relative movement along the workpiece surfaces. W

According to a preferred. embodiment of the invention the loose workingmass is kept under tool vessel preferably consists of a centrifugal'vessel or pan mounted for rotation about its gal vessel this mass underaction of the centrifus gal force forms a ring, on the freely accessibleinner part of which the surfaces of the workpiece to be treated can beput in contact with the rotary working agent. Preferably, for enlargingthe working surface, the workpiece in this case may be at least partlyimmersed in the inner annular zone of the rotary ring formed by theworking mass; if desired, it may be additionally moved, turned orswivelled for working it on all sides. By such a movement which, ifdesired, may take place in a direction contrary to the direction ofmotion of the rotary working agent, the surfaces to be treated may beacted upon by the working mass more or less intensively and/or duringlonger or shorter periods of time. The working pressure in this case mayadvantageously be regulated by suitable adjust-.

ment of the speed of rotation and/or of the diameter of the mass ringformed by the working agent. The centrifugal force determining thecompression and so the quasi consistence or hardness of this grindingring formed of the loose material is proportional to the mass of thematerial and to the square of the speed and inversely proportional tothe radius of rotation. If the speed of rotation and the diameter ofrotation are determined, the working pressure may moreover be varied byadmixing to the working material substances Whose specific gravitydiffers from that of the working agent, such as, for instance, saw dust,cork powder or the like. These admixtures may be heavier or lighter thanthe working mass and may consist of abrasive or non-abrasive materials.Further details of this centrifugal type grinding device, moreparticularly the supporting and feeding of the workpiece and theswinging thereof during the working will be hereinafter explained ingreater detail.

An apparatus designed and operated in accordance with the presentinvention permits a finishing treatment, more particularly the achievingof a grinding or polishing effect, which was not attainable by any ofthe known methods and apparatuses. Depending on the kind of the grindingmaterial or polishing substance, workpiece surfaces of any quality canbe obtained up to a beautifully ground surface with a clear reflectionat every point. The grinding efiectfollowsexactly the existing contoursso that defor- Y mations or disfigurements of the surface or ornamentsbeing thus treated are safely avoided. The surfaces disposed indifferent planes pass over into each other without any transition andwithout noticeable grinding lines. Even workpieces of an intricate shapecan be worked by the novel method and apparatus according to theinvention without any 1dimculties. The grinding capacity is extremelyincreased and the time of working reduced, since the working material isable to act simultaneously on large sur faces of the workpiece. Theworking and preferably also the feeding and removal of the workpiecesare achieved by mechanical means so that human labor is saved. Moreover,a single device,

for instance, a centrifugal grinding device, permits the simultaneousfinishing of numerous workpieces.

Other and further objects, features and advantages of the invention willbe pointed out hereinafter and :appear the appended :claims forming partof the application.

In the accompanying drawing some now preferred embodiments -.of theinvention are shown by way of illustration and not :by way oflimitation.

Fig, l is .a vertical section of a centrifugal grinding apparatusaccording .to the invention.

Fig. 2 is .a horizontal section, on the .line 2-2 of Fig. 1, through thecentrifugal vessel alone.

Fig. 3 is :a view similar to Fig. l, but showing on an enlarged scalethe mechanism marked by the .circle Fig. 1 and taken on line 33 of Fi.4; and

Fig. 4 is a horizontal section on the line 4--4 of 'Fig. 3.

A particularly advantageous and practical form of the invention can be:obtained by providing the loose mass of the working material in theform of a mass ring produced by centrifugal force, for tight engagementof the workpiece surfaces with the inner ring zone of this mass ringwhich is moved past the workpiece surfaces. embodiment of this preferredform ofzthe invention is shown in Figs. 1 to 4. The tool vessel inthis'case consists of a centrifugal tray or pan 52 provided at itscircumference and bottom with rein-forcing ribs 53 and being open in itscentral upper part. The upper pan edge '54 together with the side wall55 thereof and the outer part of the preferably conically shaped panbottom 53 forms an annular channel having a U-shaped cross section inwhich the working material H which in its state of rest lies on thebottom of the pan, is forced outwardly against the side wall of the panunder action of the centrifugal force caused by rotation of the pan. Themass of the working agent I! thus forms a mass ring of a loose,granular, powderous or pasty grinding or polishing material, which, ifdesired, may be mixed with filling substances. The centrifugal pan '52is mounted for rotation on a vertical journal or pivot 58 by means ofits hub 51, a slide bearing 59 being provided to form athrust or stepbearing. A toothed rim 60 connected to the hub 51 meshes with a pinion6i which through a reduction gear 62 is driven from an electromotor 63,whereby the centrifugal pan 52 is rotated at an adjustable rate ofspeed. Secured on the journal or trunnion 58 is a tubular member 64bearing a stationary covering plate 56 provided with perforations 65.

Secured on a foundation ring 6'. surrounding the centrifugal pan 52 witha suitable clearance is an annular carrier #68 with a hollow boxshapedcross section on which are secured at least one, but preferably several,bearing supports 69 extending radially towards the center axis of theapparatus. The bearing supports 69 are advantageously downwardlyrecessed troughfashion and at their free ends carry bearing bodies 7Gabout the horizontal axis of which the swingable arms ll serving forchucking :the workpieces are rotatable in vertical radial planes. Theworkpieces 72, for instance, spoons, are detachably secured to the heads13 of the swing- .able arms. The fastening is preferably effected withthe aid of clamping blocks M, gripping the workpieces tong-fashion, theclamping block 15 being rotatable about a shaft 76 and provided with a'lever arm ll against which presses an adjustable press bolt 18, wherebythe jaws of the clamping block are pressed against the workpiece :2clamped therebetween, as will be seen from Fig. 3.

.Since many workpieces, such as spoons and other articles of acutleryfor complete finishing have to .be rechucked in order that the surfaceschucked during .the first treatment may be brought .into contact withthe working material in a subsequent treatment, I prefer to arrangealways two swingable arms H with chucking devices side by side, .so asto form a pair. The two arms of each pair may be swingable independentlyof each other, but preferably they are simultaneously swung from theirposition of rest to their operative position. Such swingable arms orpairs of arms may be arranged at various parts of the circumference ofthe tool pan in the annular carrier $8 so that a corresponding number ofworkpieces maybe worked simultaneously.

In their position of rest the swingable arms are swung upwards :so as totake up the position indicated in dotted lines 12', '13 in Figs. 1 and3, in which position the clamping blocks 14, 7 5 are freely accessibleand the pressure screw (in this case denoted 18') can be released ortightened by means of its quadrangular end.

, After the workpiece 12 has been fixedly clamped,

the swingable arm "H is swung about the horizontal axis of the bearingbody 16 through about 270 until it comes into its operative position, inwhich the clamping blocks 14, 15 dip the workpiece 12 mor or less deepinto the inner freely exposed annular zone of the mass ring H. Theworking material being kept under pressure by the centrifugal force ismoved past the workpiece surfaces at a suitable adjustable speed. Thecircumferential speed of the centrifugal pan 52 must at least reach anamount sufiicient to urge the grinding, polishing or other workingmaterial, lying on the bottom of the pan in the position of rest, ontothe circumferenc of the pan, as indicated in the drawing.

The swingable arms Il may be swung manually, mechanically, electricallyor hydraulically etc. In the example, hydraulic pressure cylinders 19are arranged at the sides of the bearing supports 69, pressure pipes 80being provided for feeding a fluid (liquid, gas or air) to the cylinderfrom a source of such fluid under pressure (not shown). A piston 8|slidable in the cylinder 19 has at the outwardly projecting end of itspiston rod 82 a toothed rack 83 meshing with a pinion 84 secured to therotatably mounted head 85 of the swingable arm H. By forward or backwardmotion of the piston 8| in the pressure cylinder '19 the swingable arm"II is thus swung upwards or downwards.

In order to insure uniform exposure of all surfaces of the workpiece tothe impinging working material, the workpiece may additionally be swungor turned while being in an operative position. To this end, forinstance, the head 13 of the swingable arm with the clamping blocks i4,i is mounted for rotation about its longitudinal axis by means of ashaft 8? rotatably mounted in a head casing 86. The rotation of theshaft 8? may be achieved, for instance, from outside by an electromotor88 rotating, through a driving shaft 89, a worm 9t and a worm wheel 9|,a horizontal shaft 92 mounted for rotation in the swingable head orheads 85. The shaft 92 through bevel wheels 93, 9d drives one or, incase of pairs of swingable arms 1|, two intermediate shafts 95 which aremounted for rotation in the hollow swingable arms H. At its end disposedin the casing 86 of the swingable head each intermediate shaft 95 bearsa worm 96 engaging a worm wheel 9i seated on the clamping head shaft 81.

In case of workpieces such as spoons 12 there are advantageously twopairs of clamping blocks M, iii arranged at both sides of the clampinghead I3, so that the workpiece can be chucked simultaneously at twospots, e. g., a spoon at its stem and at its bowl, by swinging theswingable arm it into its operative position. The workpiece is dippedinto the grinding or other working agent H from inside and then slowlyrotated at least once about the axis of the shaft 8'! during thegrinding or polishing. Then the swingable arms I! are swung out and theworkpiece, for instance, the spoon 72, is rechucked in order that thechucked spots may be treated in a second operation. In this secondoperation the workpiece again is swung at least once about the axis ofthe shaft 81. In Fig. 3 the dotted lines '52 show one position of thisswinging motion of the spoon E2 in which it is turned through 90.

The additional rotation of the workpiece 12 about the axis of shaft 81,e. g. about an axis being disposed approximately radial to the centeraxis of the centrifugal pan, can take place at a variable speed, so thatthe working material acts uponthe workpiece for a more or less extendedperiod of time in the different angular positions of the workpiece. Thisvariable rotary motion may be controlled according to a predeterminedprogram adapted to the respective workpiece. The surfaces of theworkpiece are thus ground oif or worked partly more and partly lessintensively without producing sharply defined transition lines.

Owing to the fact that the workpiece holders, e. g., the clamping blocksM, 15, extend from insid at least approximately in the direction of thecentrifugal radius, the centrifuged working material is subject tominimum disturbance by still zones formed at the lee-side of theholders. It is also possible, however, to produce such still zones inthe flow by suitable configuration of the design of the workpieceholders so as to expose certain zones of the surface to a reducedgrinding effect.

Workpieces having curved surfaces of different inclinations passing overinto each other, such as, e. g. spoons, are advantageously held in sucha way in relation to the centrifugal axis that as far as possible allspots of the surface will successively come into an effective grindingposition during onerevolution of the workpiece about its axis. ofrotation extending approximately in the direction of the centrifugalradius. The fiat stem side of a spoon in this case may be disposed, forinstance, perpendicularly to this plane of swinging.

While the invention has been described in detail with respect to somenow preferred ex-- amples and embodiments of the invention, it Will'- beunderstood by those skilled in the art after understanding the inventionthat various changes and modifications may be made without departingfrom the spirit and scope of the invention and it is intended,therefore, to cover all such changes and modifications in the appendedclaims.

Having thus described the invention, what is claimed is:

1. A device for finishing the surfaces of workpieces comprising a panmounted for rotation about its center axis and having therein afinishing mass of abrasive and like materials only partly filling saidpan, means for rotating said pan at a speed at least sufficient to causethe formation, under action of the centrifugal force, of a mass ring insaid pan, a swingable arm and a workpiece holder arranged at the freeend of said arm and adapted to hold the workpiece, said arm beingswingable in a plane extending substantially radially and parallelly tothe centrifugal pan axis into a position where the workpiece holder isdisposed freely accessible outside of the centrifugal pan, for chuckingand removing the workpiece, and into a second position where theworkpiece fastened to the workpiece holder is disposed in the innerannular zone of the mass ring.

2. A device for finishing the surfaces of workpieces comprising a panmounted for rotation about its center axis and having therein afinishing mass of abrasive and like materials only partly filling saidpan, means for rotating said pan at a speed at least sufiicient to causethe formation, under action of the centrifugal force, of a mass ring insaid pan, a swingable arm and a workpiece holder rotatably mounted onthe free end of said arm and adapted to hold the workpiece, said armbeing swingable in a plane extending substantially radially andparallelly to the centrifugal pan axis into a position where theworkpiece holder is disposed freely accessible out side of thecentrifugal pan, for chucking and removing the workpiece, and into asecond position where the workpiece fastened to the workpiece holder isdisposed in the inner annular zone of the mass ring, the axis ofrotation of the holder being disposed substantially perpendicularly tothe swingable arm and, in the second position thereof, in a directionsubstantially radially to the centrifugal pan axis.

3, A device for finishing the surfaces of workpieces, comprising a panmounted for rotation about its center axis and having therein afinishing of abrasive and like materials partly filling said pan, meansfor rotating said pan at a speed at least suificient to cause theformation, underaction of the centrifugal force, of a mass ring in saidpan, a number of swingable arms nonrotatably arranged around theperiphery of the rotatable pan, and workpiece holders arranged at thefree end of said arms and adapted to hold the workpiece, said arms beingswingable in planes extending substantially radially and parallel to thecentrifugal pan axis into a position where the workpiece holders aredisposed freely accessible outside of the centrifugal pan for chuckingand removing the workpieces, and into a second position where theworkpieces fastened este m rtq the workpiecehcldersare.disposed intheinner n u one of the irnass ring". 54. A device ,for iinishina. the;surf aces ofMworkpieces, comprising a pan mountedI-fortrotatibn aspegedat least sufiicient- .to ca se the.-formation, under action of thecentrifugal iorce iofi a-mass ring said span anumber; ofiswzmgable arms:dis-

tr buted around the, -periphery.-.of lthe rotatable .nan QR. c rr in.rinesurr undina h ss p with a clearance, eachfiffiaid arms havingiaworkpiece holder rotatably mounted on theifree ,end ofsaid arm and;adapted .to-holda workpiece,

each of said arms being swingable in aplaneeiztending substantiallyradially, and. parallel. to the centrifugalaxis-of the panintotatposition where h wp n e holderis disposed freely accessibleoutside .ofthe centrifugal pan for chucking and removing the workpiece,and into a secondposition; where the workpieceiastened to the ,workpieceholder is dispo ed inthe inner annular zone of the mass ring, the axisofrotationof the workpi e h der vbeingdisposed Substantially ne,pendicularly to the .SWingable, armand, in the second position thereof,.in,.a 'd', .ection. substantially radially to thecentrifugal pan axis.

r 5. Adevice rforefinishingrthe.surfaces of workpieces, comprisingeaipanmounted for rotation about. its center axisand. having thereinafinishing, mass of abrasive andZlikeimaterialspartly filling said pan,-means: for. rotating; said panata speed at. least .suificientetocausetheiformation, under actionof the centrifugal fo'rce, ofai-massring insaid pan,.at.least= one pair of. .swingable arms arranged sideby.side, .both. armsof the .said pair having; a workpiece holder arrangedeach, at the free. end of. each of .said.arms andadapted to holdthe.workpieceieach, arm being swingable in. a plane extending substantially.parallelsto a plane extending radially. and parallel .to. the.centrifugal axis. of thepaninto. a position where @the workpiece holderis disposed freelyaccessible outi e; .1the .centrifuga1 pan ,forJchucking'and .removing theiworkpiecei andinto agseconcl position where,.-the workpieceifastenedito. the. workpiece holder is at vleast partly;immersed: in. the rotating mass, ring of; finishingmate'rial.

6.1-A. deviceefor finishing the surfaces of 1 workpieces, comprisinga-..pan .mounted; for rotation about. its center axis. andhaving thereinafinishns mas of abrasive; and like; materials partly filling; said;pan, ,means; for -rotat.ing-, said .pan at a speed at least sufficient.to. cause; the; formation,

under actionoi-the.centrifugahforce, of a-.;mass= ring of loosefinishing materials.-in-,, aid pan, at least one pair. of..-.swingablejarms; arranged side by-side, each-of saidarms having ,a,,workpieceholder rotatably mcunted on the: free end ,ofsaid arm and adapted toholdv aworkpiecaeach ofsaid arms being swingable, in; ,a planesubstantiall parallel to. a plane extendingradiallyand parallel togthecentrifugal axisof the pan intoa; position where the, workpiece hold-er;is.-disposed.,free1y accessible outsideof the centrifugal panforchuckingand removi ngthe workpieces, and in a second position where;the .workpiece'iastened to the workp r o der is-h ld in -the-peih-o imove en of.-the-ro.tating massiring of finishingmaterial.

- '7,-- A device forfinishing-the surfacesofworkpieces; comprising a paninounted for rotation aboutits central yertical ;-axis and being adaptedto contain therein a fipishing ma as abr sive and like rnaterials onlypartly filling said pan,

r-nieansfor rotating said pan at a speed at least "sufiicient to i causethe -formation, under action of the centrifugaliorce, of amass ringofabrasive and like" materials in said pan, the pan having'a peripheralwall concentric with theaxis 0': rotaticn'and provided on its upperedgewith a concentric annular; inturned cover portion, a

stationary carrying ring surrounding the centrifuge pan with aclearance, bearing supports secured on-the calrying ring, workpieceholders rockablylniofinted on' thesaid bearing supports and provided ontheiriree ends with means for de tah'hably securing-the workpieces, saidworkpiece holders being rockabl e in substantially radial verticalplanes independentl ygof oneanother and into a position :where' theworkpiece holder-is disposed-freely accessible outside of thecentrifugal pan, for chucking and removing the workpieces, and intoat'least one other position where the war-apiece fastened to the workpieceholder is dispose'd in the path of movement of the rotating mass ring ofabrasiveand like materials;

A'device for'finishing the surfaces of workpieces, comprising amber-g;container adapted to bepartly filled with abrasive and like materialshavinga peripheral can concentric with the axis o'f" ';1 'otation, ansf'o'r revolving said container at a speed sufiicint to cause, underaction of the centrifugal forc'e} the formation of amass ring ofthe saidabrasive and like materials against said "peripheral walh workpieceholders stationa rily arranged around the periphery of the container,each wo riqo i'c'e holder being swingable in a planeextending-substantially vertically trend the peripheryt'o the middlezone of the container into a' "positio'ntwherethe workpiece holder isdisposed freely accessible outside of the'container f o'r chucking andrenioyinga workpiece, and me a second position l fibre th workpiecefastened to the "free ens of the swingalole workpiece holder is atleastpartially heldin the path of movement Of-the r tatln ginass' ring orabra siv andthelike naterials.

i 9. a A device 'forfiinis h'ihg the surfaces of Workpieces, comprisingrotary container 'mounted for rotation about a verticarcentral axis andhavingfitherein' a' finishing mass 'of abrasive and likernaterails onlypartly filling said container, for rotating said container at aspe a atleast" oient fo 7 causeithe forrnation, under action of 'the' centrifgalfforce, ofa 'mass ring of abrasive andflike rnaterials againstjaperipheral wall" of the container concentric with 'the axis of rotation,atleast one swingable arrn and a workpiece holder rotata' bly rno untedonlthe free end oi s-aid arm and adapted to hold the workpiece, the axisof rotation of the holder be di po su s ntial p r ndi ar y to theswmgable arm, said a'rm, heing swingable in air a 1 concentric annularcover portion, means for rotating said container at a speed at leastsufficient to cause the formation, under action of the centrifugalforce, of a mass ring of abrasive and like materials in said containeragainst the peripheral wall, pairs of workpiece holders stationarilymounted and distributed around the upper periphery of the rotatingcontainer, said Workpiece holders being adapted to hold the workpiecesat their free ends and being rockable each in a plane substantiallyvertical and extending from the periphery of the container to the middlezone of the container from outside the container into the interior ofthe container where the workpieces are held at least partly immersed inthe stream of abrasive material forming said mass ring.

11. A device for finishing the surfaces of workpieces, comprising acontainer mounted for rotation about its vertical center axis and havingtherein a finishing mass of abrasive and like materials partly fillingsaid container, means for rotating said container at a speed at leastsufficient to cause the formation, under the action of the centrifugalforce, of a mass ring in the container, the base of the said containerhaving a frustro-conical inclined part adjacent its periphery, at leastone swingable arm and a workpiece holder arranged at the free end ofeach arm and adapted to hold the workpiece, each arm being swingable ina plane extending substantially radially and parallel to the centrifugalcontainer axis into a position where the workpiece holder is disposedfreely accessible outside of the centrifugal container for chucking andremoving th workpiece, and into a second position where the workpiecefastened to the workpiece holder is at least partly held in the path ofmovement of the abrasive material forming the mass ring.

12. A device for finishing the surfaces of workpieces, comprising acontainer mounted for rotation about its center axis and having thereina finishing mass of abrasive and like materials partly filling saidcontainer, means for rotating said container at a speed at leastsufficient to cause the formation, under action of the centrifugalforce, of a mass ring in said container, at least one pair of swingablearms arranged side by side and workpiece holders arranged at the freeends of said arms and adapted to hold the workpieces, both arms of thepair being adapted to be rocked together in a plane extendingsubstantially radially and parallel to the centrifugal container axisinto a position where the workpiece holders are disposed freelyaccessible outside of the centrifugal container for chucking andremoving the workpieces, and into a second position where the workpiecesfastened to the workpiece holders are at least partly held in the pathof movement of the abrasive and like materials forming the mass ring.

13. A device for finishing the surfaces of workpieces, com-prising acontainer mounted for rotation about its center axis and having thereina finishing mass of abrasive and like materials only partly filling saidcontainer, means for rotating said container at a speed at leastsuflicient to cause the formation, under action of the centrifugalforce, of a mass ring in the said container, at least one pair ofswingable arms arranged side by side, and a workpiece holder rotatablymounted on the free end of each arm and adapted to hold the workpiece,the arm of each pair being swingable together in a plane extendingsubstantially radially and parallel to the centrifugal container axisinto a position where the workpiece holders are disposed freelyaccessible outside of the container for chucking and removing theworkpieces, and into a second position where the workpieces fastened tothe workpiece holders are at least partly immersed in the mass ring.

14. A device for finishing the surfaces of workpieces, comprising acontainer mounted for rotation about its center axis and having thereina finishing mass of abrasive and like materials only partly filling saidcontainer, means for rotating said container at a speed at leastsufficient to cause the formation, under action of the centrifugalforce, of a mass rin in said container, at least two workpiece holdersadapted to hold the workpieces, said workpiece holders being movableindependently of one another into a position where each workpiece holderis disposed freely accessible outside of the centrifugal container, forchucking and removing the workpiece, and into a second position wherethe workpiece fastened to the workpiece holder is at least partly heldin the path of movement of the mass ring.

15. A device for finishing the surfaces of workpieces, comprising a panmounted for rotation about its central vertical axis and havin therein afinishing mass of abrasive and like materials partly filling said pan,means for rotating said pan at a speed at least sufficient to cause theformation, under action of the centrifugal force, of a mass ring offinishing material in said pan, a plurality of swingable arms mounted onbearing supports arranged stationarily around the periphery of the pan,a workpiece holder arranged at the free end of each swingable arm andadapted to hold the workpiece, each of the said arms being swingableindependently of one another on a stationary pivot pin mounted on thesaid bearing support in a plane extending substantially vertically fromthe periphery to the middle zone of the centrifugal pan into a positionwhere the workpiece holder is disposed freely accessible outside of thecentrifugal pan, for chucking and removing the workpiece, and into asecond position where the workpiece fastened to the workpiece holder isdisposed in the path of movement of the rotating mass ring of finishingmaterial.

PAUL K. A. CUPPERS.

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